Method for manufacturing nonwoven sheet material

ABSTRACT

D R A W I N G A METHOD AND APPARATUS FOR MAKING NONWOVEN SHEET MATERIAL IN WHICH ENDLESS FIBERS ARE SPREAD APART FORM EACH OTHER INTO A FIBER MAT, THEN IMMERSED IN A FORMING MEDIUM, CUT INTO FIBERS OF FINITE LENGTH AND FORMED INTO A SHEET ON A PERMEABLE SUPPORT EITHER ALONE OR WITH TRADITIONAL SHORT FIBERS SUCH AS CELLULOSE OR GROUND WOOD FIBERS. THE ENDLESS FIBERS ARE PROVIDED IN A BUNDLE WHICH IS BEATEN TO LOOSEN THE FIBERS BEFORE THE SPREADING STEP AND THE SPREADING IS ACCOMPLISHED EITHER BY EXPOSING THE FIBERS TO AN ELECTRIC FIELD OR BY ONE OR MORE AIR CURRENTS OR BOTH. THE FIBERS ARE CUT WHILE IMMERSED IN THE FORMING MEDIUM (FOR EXAMPLE, WATER) BY A PLURALITY OF REPLACEABLE KNIVES MOUNTED ON A ROLLER AND A COUNTERKNIFE. THE KNIVES ARE SPACED ABOUT THE CIRCUMFERENCE OF THE ROLLER AT VARIABLE DISTANCES SO THAT WHEN THE ROLLER IS ROTATED THE FIBERS ARE CUT INTO DIFFERENT LENGTHS.

Sept. 12, 1972 F, OPDERBECK EI'AL 3,691,009

METHOD FOR MANUFACTURING NONWOVEN SHEET MATERIAL Filed Jan. 12. 19705932mm on o 22 2 Iuu2 United States Patent Oflice many Filed Jan. 12,1970, Ser. No. 2,307 Claims priority, application Germany, Jan. 11,1969, P 19 01 285.2 Int. Cl. D21f 11/00; D21h 5/12 US. Cl. 162-146 11Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for makingnonwoven sheet material in which endless fibers are spread apart fromeach other into a fiber mat, then immersed in a forming medium, cut intofibers of finite length and formed into a sheet on a permeable supporteither alone or with traditional short fibers such as cellulose orground wood fibers. The endless fibers are provided in a bundle which isbeaten to loosen the fibers before the spreading step and the spreadingis accomplished either by exposing the fibers to an electric field or byone or more air currents or both. The fibers are cut while immersed inthe forming medium (for example, water) by a plurality of replaceableknives mounted on a roller and a counterknife. The knives are spacedabout the circumference of the roller at variable distances so that whenthe roller is rotated the fibers are cut into diiferent lengths.

BACKGROUND This invention pertains to a method and apparatus formanufacturing nonwoven sheet material. More particularly it relates to amethod and apparatus for making such material using a process in whichtextile fibers either alone or with other fibers are formed into a sheeton a support with the aid of a forming medium.

It is known that the strength and pliability of paper increases with thelength of the fiber(s) used in its construction. Thus, while shortcellulose and ground wood fibers from 5 to 6 mm. long are commonlyemployed in making paper, longer length fibers, sometimes called textilefibers, are used in making high strength and pliable papers. Forexample, cotton linters have long been used in manufacturing very highgrade paper. Recently comparatively long synthetic fibers made ofregenerated cel lulose or synthetic plastic have been used in makingpaper-like sheet materials of heretofore unattainable tensile strength.

-In addition, recent technological developments have made fluid the lineof demarcation between ordinary fabrics and knit goods on the one handand paper and cardboard on the other. Thus, nonwoven sheet materialsmade of comparatively long fibers of finite length are increasinglyreplacingtraditional fabrics and knit goods. For example, it is known toarrange the fibers in these materials in a random fashion and that thelonger the fiber(s) used the more closely do the properties of thematerials, especially their pliability and hang (i.e., drape), approachthat of ordinary fabrics and knit goods.

Heretofore, however, manufacturing techniques have restricted to use ofcut fibers in nonwoven sheet materials to lengths not exceeding about 20mm., and this is particularly true when the fibers were dispersed inwater and formed into a sheet on a water permeable screen or support.The reason is that fibers longer than about 20 mm. bunch up and formknots in water and make the resulting product wild and nonuniform. ThesePatented Sept. 12, 1972 ditficulties can be partially overcome bydispersing the fibers in larger and larger quantities of water, but thistechnique becomes increasingly'uneconomical and entails a very dilutesuspension which requires the use of tremendous quantities of water.

It is also known to use endless fibers (i.e., continuous filaments orcapillaries) in making nonwoven sheet materials, but between endlessfibers and fibers of a short finite length there lies an intermediateregion that has not been utilized technologically up to now. Thisintermediate fiber length region promises to provide interesting newsheet materials with characteristics that can bridge the gap betweenproducts made of endless fibers and those of short finite length.

SUMMARY OF THE INVENTION The invention comprises a process and apparatusfor making nonwoven sheet materials wholly or in part from textilefibers (i.e., fibers whose length is in this intermediate region). Theprocess is characterized by the steps of spreading a multiplicity ofendless fibers out into a fiber mat, cutting the fibers into finitelengths immediately after which they are formed into a sheet on asupport with the aid of a forming medium. The fibers are preferablyprovided in a continuous skein or bundle, and are stretched before beingcut into finite lengths. The fibers are spread out into a fiber mateither by charging the fibers electrically or by applying one or morecurrents of a gas such as air which also stretches the fibers. Thespreading may also be promoted by mechanical means if desired. Thefibers are then immersed into the forming medium and cut into lengths.This medium may comprise either a liquid or a gas such as, for example,air or water. The process also includes not only forming the sheetmaterial with textile fibers in the above described manner, but inaddition the step of using fibers of differing properties in itsformation. For example, short cellulose or ground wood fibers may beadded to the textile fibers. When air is used as the forming medium abonding agent may also be applied to the textile fibers to improve thecharacteristics of the sheet.

One advantage of the process according to the invention is that itfacilitates cutting of the endless fibers into differing finite lengths.Heretofore endless textile fibers having the fineness of an endlesscapillary (such as is obtained in the manufacture of synthetics) havebeen difficult to cut successfully when gathered into a skein. The heatand pressure produced at the cutting edge of the knives, particularlywhen the fibers were made of thermoplastic materials, preventedsatisfactory separation of the fibers during their subsequent dispersionin air or in water and resulted in formation of agglomerations ofseveral fibers which created defects in the sheet material. 'Byimmersing the textile fibers in the forming medium, particularly whenthis medium is a liquid such as water, and then cutting the fibers inthe medium the heat from the cutting step is carried away more quicklyand fewer agglomerations of the fibers are formed. In addition, byhaving the fibers cut in a flowing stream of water they are reliablycarried oil by the water, thus greatly prolonging the life of the knivescutting edge.

Another advantage of the inventive process is the fact that the fibersare spread out into a fiber mat before they are cut into finite lengths.By spreading them out and immersing them in the forming medium beforecutting them, disturbances associated with transitions from one mediumto another, which are very likely to occur with fibers of finitelengths, are avoided. In addition, the spreading of the fibers insuresthat when cut they do not have to be distributed by stirring oragitation, or the like, prior to formation of the sheet material.Instead, they are already present in the medium in the idealdistribution as individual fibers.

In one preferred embodiment the inventive apparatus comprises means forcarrying out the inventive process wherein the fiber mat is immersed inthe forming medium and fed to a cutting device which comprises aplurality of knives mounted on a roller. Preferably the knives areinterchangeable and are spaced circumferentially apart at variabledistances so that fibers of different lengths may be cut with the sameroller with a minimum of change in the position of the knives.Preferably also, the knives are positioned over the width of the rollerand are circumferentially spaced at different distances from each otherover this width. This makes it possible, for example, to cut longer andshorter fibers alternately over the width of the roller so that thefibers are cut into different lengths.

A second preferred embodiment of the cutting device according to theinvention comprises a plurality of beater knives and a stationarycounterknife. This embodiment is especially suited for working underwater. With a device of this sort the length of the fibers can beregulated practically from infinite length to short fibers only a fewmm. long by varying the number of beater knives and/or their r.p.m.

In bigger and wider installations it is entirely feasible to employseveral cutting devices of either or both of these embodiments at thesame time with each device having different knife spacing or differentr.p.m. so that fibers of different lengths can be cut and fed to thesheet forming support. It is also contemplated that in some embodimentsthe knives exhibit interruptions over their entire length so that someof the endless fibers are not cut at all but are fed to the support asendless fibers as an aid in forming the sheet material. In this waysheet material can be made largely of fibers of finite length, but willalso include some endless fibers as a reinforcement in a singleoperation without requiring additional apparatus.

Sheet materials made by the inventive process have a very soft feel andgood textile hang qualities. They are particularly suitable for themanufacture of clothing, underwear, diaper wrappings, tampons, sanitarynapkins, curtains and bed linens. Other further and additional objects,features and advantages of the invention will be apparent from thefollowing description of the invention in connection with the drawingsand the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic elevation viewof one preferred embodiment of the apparatus according to the invention;

FIG. 2 is a schematic plan view of the left-hand portion of theapparatus of FIG. 1;

FIG. 3 is a detailed schematic elevation view of one embodiment of thecutting apparatus of the invention;

FIG. 4 is a plan view generally along line 44 of FIG. 3; and

FIG. 5 is a detailed schematic view elevation of a second embodiment ofthe cutting apparatus according to the invention.

DETAILED DESCRIPTION Referring now more particularly to FIGS. 1 and 2 ofthe drawings, when the endless fibers are synthetic the process alsopreferably includes a stretching step in which the fibers are stretchedto optimize their strength. When the fibers are provided in the form ofa bundle or skein 11 on a reel 14 the stretching may be accomplished bya roller 16 which applies a stretching force to the bundle 11 by meansof a spring 18 through a suitable linkage 20. The tension of the spring18 may be adjusted to apply the desired stretching force to fibers inthe bundle or skein 11 before they are spread out into a mat.

In addition, though not shown in the drawings, when the endless fibersare synthetic and are to be spread electrically, if they are not usedimmediately after they have been produced, it is advisable to pass themthrough a solvent such as petroleum ether to strip off any antistaticcoating which may have been previously applied to them. Removal of thiscoating facilitates the electrical spreading step.

The process of the invention can be varied within wide limits to achievesheet materials having certain desired properties. Thus, in one aspectthe process includes subdividing the endless fibers into differentlengths. For example, sheet material made by the process may include apercentage of fibers of considerable length, say 50 mm., while the restof the fibers are cut into shorter lengths. The resulting product hasconsiderable strength and satisfactory textile hang properties andcomprises a highly uniform and comparatively thick material.

In another aspect the process includes adding short fibers such ascellulose or ground wood to the forming medium prior to or during theformation of the sheet material. In this way the properties of thematerial can be varied. In addition, the addition of thermoplasticbonding fibers which partly fuse during the subsequent drying of thesheet material produce a supplementary bond which increases the strengthof the sheet and has proved to be highly desirable. Such bonding fibersmay, for example, comprise either textile fibers or additional shortfibers to which a bonding agent has been added.

In principle, two basically known methods may be employed to form thesheet material by the process of the invention. Forming may be done withthe assistance of a gas such as air which serves to deposit the finitelength fibers (after they are cut) on a permeable support preferablycomprising a bronze or plastic screen. When the material is thus formeda bonding agent may be easily applied to the fibers, for example, byspraying, so as to connect primarily the points where the fibersintersect. This provides additional strength to the sheet materialwithout impairing its porosity and pliability. When air is employed informing the sheet material it has been found advantageous to use anelectric field to align the fibers in certain 3 dimensional directions.

The process of the invention is especially useful when the sheetmaterial is formed with the aid of a liquid such as water.

[Referring again to FIGS. 1 and 2 of the drawings, the preferredembodiment of the apparatus according to the invention includes a fiberbundle feeding mechanism comprising a pair of rolls 22, 24 which arecovered with a soft type of gum 26 having a shore hardness of about 40degrees. The function of the gum surface is to grab onto the bundle 11and feed it to the beater mechanism 30. Instead of gum any suitable softmaterial such as, for example, plastic, which will perform the samefeeding function, may also be used. One of the rolls 22, 24 is driven bya conventional variable speed drive device (not shown) and power to theother roll is transmitted by contact friction between the rolls. Aspring biased mechanism (not shown) may be provided to keep the rolls incontact with each other and yet permit the distance between theircenters to be automatically adjusted by the diameter of the bundlepassing between them. The variable speed device is not absolutelyessential, but it does serve to adjust the speed of advance of thefibers to the speed of the fourdrinier wire screen support 32 on whichthe sheet material 34 is formed. Rolls 22, 24 are not intended toperform any fiber spreading function, but together with tension roll 16and delivery rolls 44, 46 which will be referred to hereinafter they docreate a certain amount of tension in the area in which the fibers arespread apart from one another.

From the feed rolls 22, 24 the fiber bundle 11 is fed to the beatermechanism 30 which preferably comprises a magnetically driven beater 36and a stop plate 38. Beater 36 is preferably operated by the standard220 volt power available from utility companies and operates at thefrequency of this power, for example, at 60 cycles. Different voltagesand higher or lower frequencies may also be used, if desired. With atypical fiber bundle 11 the stop plate 38 is positioned about 1 inchbelow the bundle and the beater 36 about 2 inches above the bundle. Theprincipal fuction of the beater is to pound down onto the bundle 11 toloosen up the fibers 10 to facilitate their being spread apart. Only ifthe fibers are already loose and quite parallel will this deviceaccomplish any significant spreading.

From the beater the bundle 11 is fed to the spreading section of theapparatus which, depending on the nature of the fiber being spread,comprises a mechanical spreader 39, an air spreader 40 and an electricfield generating device 42. It is known to spread endless textile fibersout into a fiber mat by electrically charging the fibers with the samecharge so they repel each other. Electrical spreading device 42 whichaccomplishes this function includes an electrode 43 which, for example,if the electrical resistance of a single fiber is about 10 ohms, may becharged to 5000 volts. If the ohmic resistance of the fibers is higher,for example, 10 ohms, 30,000 volts or more on the electrode may be used.If the ohmic resistance of the fibers is 10 ohms or less, the chargewill leak off and little, if any, separation will occur. To keep theohmic resistance of the fibers as uniform as possible any electricalspreading should be accomplished before any air spreading. The humidityof the air in such a spreader will aifect and may reduce the electricalresistance of the fibers. If the fiber diameter is between about 1.2 to4 or 5 desitex, other conditions being appropriate, the fibers arelikely to be adequately spread apart by exposure to an electric field ofappropriate strength for a period of about A second.

From the electrical spreader the fibers pass between a second pair offeed rolls 44, 46 which are similar to rolls 22, 24 previously describedand are driven at approximately the same speed. Just before rolls 44, 46there are a pair of guide rods 48, 50 provided to reduce the verticalspread between the fibers so they will feed properly between the rolls.This feature is particularly useful where the apparatus does not includean air spreading device. As they pass between the rolls 44, 46 thefibers 10 form a mat of individual substantially parallel capillariesspaced apart along the length of rolls in a mat having substantially thesame width as the sheet forming support 32 from rolls 44, 46. Asillustrated in FIG. 1 rolls 44, 46 are grounded as an aid to theelectrical spreading step. From these rolls the fibers 10 pass down achannel 52 through the lower portion of the liquid channel 54 that leadsto the sheet forming support or fourdrinier wire 32. The water flowingthrough the channel 54 conveys the fibers from channel 52 to the fibercutting device portion 56 of the apparatus.

As illustrated in FIGS. 3 and 4 the cutting device comprises a pluralityof knives 58 replaceably mounted on a roller 60 and spaced apartvariable distances about the circumference of the roller so that fibersof different lengths may be cut with the same roller with a min mum ofchange in the position of the knives as the roller 1s rotated by a motor62. Each knife in turn passes ad acent a counterknife 64 and as itpasses severs the fibers positioned between these elements. The cuttingdevice is enclosed in a housing 65 through which water from channel 54passes. The motor 62 preferably is a variable speed device which isconnected to roll 60 so as to rotate it at the desired speed.

As illustrated in FIG. 4 the knives may include interruptions 66 alongtheir length so that some of the endless fibers are not cut at all. Inaddition, the knives 8 are distributed over the width of the roller 60and are circumferentially spaced at different distances from each otherover this width making it possible for fibers of different length to becut over the width of the roll so that the sheet material includesfibers of more than one length.

Referring now more particularly to FIG. 5 the second embodiment of thecutting device 56 comprises a plurality of beater knives 68 mounted on aroller 69 and one or more stationary counterknives 70. The number andspacing of the heaters may be varied to regulate the cut length of thefibers. In addition, the beater knives driven by a variable speed device(not shown) which rotates the knives at variable speeds to also regulatethe cut length of the fibers. Knives 68, roller 69 and counterknives 70are all enclosed within a watertight housing 71 through which water fromconduit 54 flows.

After having been cut into finite lengths in the Water and while spreadout into a mat the individual fibers lie separated from each other anddo not have to be distributed by stirring or the like but are present inthe medium in the ideal distribution for formation of the sheetmaterial. Thus, as additional water fiows through channel 54 they aredeposited on the inclined permeable support 32 comprising a screen.Ordinary short fibers made of cellulose are supplied to the headbox 72through conduits 74, 76 in the form of stock or pulp water whichtogether with the water in channel 54 is pulled through the screen bysuction boxes 78, 80. In this way a 3 layered nonwoven sheet material isformed with cellulose fibers on one side, textile fibers in the middleand cellulose fibers on the other side.

When air is used in forming the sheet material instead of water it hasbeen found advantageous to align the cut fibers electrically by exposingthem in certain instances to the action of an electric field.

In addition, regardless of whether a gas or a liquid is used as theforming medium, the width and the speed of movement of the mat of spreadfibers preferably corresponds to the width and speed of the permeablesheet material forming support.

The terms and expressions which have been employed herein are used asterms of description and not of limitation. There is no intention in theuse of such terms and expressions of excluding any equivalents of thefeatures disclosed or portions thereof and it is realized that variousmodifications are possible.

What is claimed is:

1. A process for making nonwoven sheet material at least in part fromtextile fibers, comprising the steps of spreading a plurality of endlessfibers out into a fiber mat in which the fibers are parallel to eachother, thereafter immersing the fibers in water followed by cutting thefibers immersed in the Water into textile fibers and then forming thesefibers into sheet material on a support with the aid of the water andthereafter drying the material.

2. A process according to claim 1 including the step of stretching theendless fibers to optimize their strength before cutting them.

3. A process according to claim 1 wherein the spreading step includesthe step of charging the endless fibers electrically to spread them outinto a fiber mat before being immersed in the water and then cut.

4. A process according to claim 3 wherein the step of charging theendless fibers electrically comprises the step of passing them throughan electric field.

5 A process according to claim 1 including the step of applying at leastone current of air to the endless fibers to spread them out into a matbefore immersing them in the water and cutting them.

6. A process according to claim 1 wherein the spreading step includesthe step of pounding the endless fibers with a mechanical device andthereafter the step of applying at least one current of air to thepounded endless fibers to spread them out into a mat.

7. A process according to claim 1 wherein the cutting step includes thestep of cutting the endless fibers into textile fibers of differinglengths.

8. A process according to claim 1 including the step of adding shorterfibers to the water to form the sheet material from both the cut textilefibers and the shorter fibers.

9. A process according to claim 3 wherein the shorter fibers comprisenatural short fibers selected from the group consisting of cellulose andground Wood.

10. A process for making nonwoven sheet material at least in part fromtextile fibers, comprising the steps of passing a bundle of endlessfibers through an electric field to spread them apart into a fiber matin which they lie substantially parallel to one another, promoting thisspreading by pounding them with a mechanical device, immersing the thusformed fiber mat into water and thereafter cutting the fibers in thewater followed by forming the resulting textile fibers into sheetmaterial by applying them to a porous screen through which the water isdrained and thereafter drying the material.

11. A process according to claim 10 wherein the fibers are cut intodilferent lengths and natural short fibers are added to the cut fibersas they are formed into the sheet material.

References Cited UNITED STATES PATENTS 3,002,880 10/1961 Schonberg etal. 162157 3,016,599 1/1962 Perry 162146 X 3,047,455 7/1962 Holmes etal. 162-157 3,067,087 12/1962 Gorski et a1 162-157 3,328,383 6/1967Roscher et a1 264122 X 3,341,394 9/1967 Kinney 161-72 3,489,643 1/1970Hoffman 162-446 FOREIGN PATENTS 820,785 9/1959 Great Britain 162146 S.LEON BASHORE, Primary Examiner F. FREI, Assistant Examiner US. Cl. X.R.

